Minnesota I-35 Bridge Collapse Anniversary: How Safe Are Drivers Now?

Five years ago today more than 100 cars were traveling over a bridge on I-35W during a Minneapolis rush hour when it suddenly collapsed, dropping cars from the interstate into the 15-foot-deep Mississippi River below, trapping many passengers inside. Before they could escape or emergency help arrived, 13 people died and another 145 were injured one of the worst bridge disasters in U.S. history.

A formal investigation took more than a year, but once it was finished the National Transportation Safety Board said the cause of the I-35W Mississippi River bridge tragedy was a simple design flaw in the bridge's gusset plates -- metal plates that help connect one steel beam to another. At that time, NTSB acting chairman Mark Rosenker said the board's investigation would "provide a roadmap for improvements to prevent future tragedies."

But five years after the collapse, Andrew Hermann, the president of the American Society of Engineers, told ABC News that while the nation has an aggressive bridge inspection program, the government is still not spending enough money on updating and maintaining the nation's infrastructure.

"Congress basically lacks the courage to do what is needed to raise the funds," he said. "Bridges require maintenance, and maintenance and rehabilitation require funding... Politicians like to show up and cut a ribbon on a brand new bridge, but they don't like to show up and applaud a new paint job that may increase the life of a bridge."

At the time of the Minnesota bridge collapse, ABC News reported that the bridge had already been classified as "structurally deficient," meaning that while it was not deemed unsafe enough to close, it did require maintenance.

According to the Department of Transportation, bridges can be put on waiting lists for "replacement or rehabilitation" if they are classified as structurally deficient or "functionally obsolete;" the latter meaning the bridge was built prior to modern standards but was not necessarily unsafe. A common example of a functionally obsolete bridge is one with road lanes that are too narrow.

When the Minnesota bridge collapsed in 2007, approximately 25.4 percent of the nearly 600,000 bridges in the U.S. were considered either structurally deficient or functionally obsolete, according to the DOT. By 2011, the number dipped to 23.8 percent, still leaving nearly 150,000 bridges in the same categories.

But transportation officials stressed that it does not mean American drivers are traveling on thousands of unsafe bridges -- just ones that may need some type of repair or more frequent inspections.

The Federal Highway Administration "has implemented measures to more closely oversee the inspection process and identify inconsistencies and non-compliance," FHA Administrator Victor Mendez told ABC News. "While there are a number of bridges that are typically more closely monitored than others based on their condition, they are structurally safe. Unsafe bridges are closed."

The FHA said that bridges are generally inspected once every two years, depending on the bridge's age and traffic patterns.